There are over 150,000 cases of metastatic brain tumors annually, with a prognosis of about 6-8 months. Conventional treatment options, including radical surgery, radiation therapy and stereotactic radiosurgery, are often accompanied by systemic side effects, long hospital stays and morbidity. Surgical resection is not always possible because of tumor location. Stereotactic radiosurgery (SRS), while an almost ideal approach for minimally invasive therapy, runs the risk of acute radiation toxicity and radiation necrosis, accompanied by prolonged mass effect, treated generally by steroids. The hypothesis of our proposal is that laser-induced interstitial thermo-therapy (LITT) under MR-guidance and monitoring can be an effective treatment for cerebral metastases compared to SRS, with excellent local control of the treated area, fast resolution of mass effects, decreased steroid intake and subsequent quality-of-life factors. In the two years of this study, an internal pilot study will be carried out, in a prospective, randomized fashion, on 30 patients with metastatic tumors (< 3 cm), half of which will be treated with SRS and the other half with MR-guided LITT. Specific Aim 1 is to develop the use of laser to ablate brain tumors under MR guidance. Using novel temperature sensitive MRI sequences and an off-line computer monitor interface (developed here), the physician can view in a near real-time mode and without open resection, the zone of ablated cancer tissue as it is created by laser energy deposition, providing an unique noninvasive and precise method to monitor and control the extent of heat distribution. Specific Aim 2 will evaluate the comparative efficacy of the two treatment options by prolonged follow-up with MRI and other tests for the next two years. These investigations will yield outcome variables such as local control of lesion, steroid intake and quality-of-life factors, allowing a multivariate analysis based on different prognostic factors to stratify the efficacy of the two different treatment arms. The other will treat those with evidence of treatment failure by one technique. A future Phase II trial with a much larger patient cohort will be proposed with modifications dictated by this internal pilot study. The PI and his team have been one of the pioneering groups in the development of interventional MRI, with one of the most extensively used instruments utilized in the IMRI named after one of them (the Lufkin needle). If successful, this technique will offer a less invasive and possibly more effective alternative to surgical resection and stereotactic radiosurgery of not only metastatic brain tumors but to tumors elsewhere in the body and have the potential for significant improvement in cancer management in general.